The present disclosure relates to batteries and in particular to metal-gas based batteries where reactive gases are supplied by a combustion engine.
Lithium (Li)-air batteries are a form of metal-air battery chemistry that uses the oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow. Li-air batteries have high energy density compared to other types of batteries. Energy density is a measure of the amount of energy a battery can store for a given volume, and the Li-air battery comes far closer than other types of batteries to that of traditional gasoline powered engines. Li-air batteries achieve a high energy density through the use of oxygen from the air instead of storing an oxidizer internally.
The relatively high energy density of Li-air batteries has made Li-air batteries an attractive candidate for use in automotive applications. The energy density of gasoline is approximately 13 kWh/kg, which corresponds to 1.7 kWh/kg of energy provided to the wheels of a vehicle when accounting for losses. The theoretical energy density of lithium-air batteries is 12 kWh/kg excluding the oxygen mass, with a corresponding theoretical practical energy density of 1.7 kWh/kg at the wheels of an automobile when accounting for over-potentials, other cell components, battery pack ancillaries, and the higher efficiency of electric motors versus combustion engines. Thus, Li-air batteries provide a similar capability to power a drive train of a vehicle as a gas powered combustion engine.
The operation of a lithium-air battery is generally characterized by lithium being oxidized at the anode forming lithium ions and electrons. The electrons follow an external circuit to do electric work and the lithium ions migrate across an electrolyte to reduce oxygen at the cathode. When an externally applied potential is greater than the standard potential for the discharge reaction, lithium metal is plated out on the anode, and oxygen O2 is generated at the cathode. The reaction at the anode generated by electrochemical potential forces the lithium metal to give off electrons as per the oxidation. The half reaction is Li⇄Li++e−. FIG. 1A illustrates the prior art charge cycle of a Li-air battery, with electrons traveling to the anode and oxygen being released at the cathode. FIG. 1B illustrates the prior art discharge cycle of a Li-air battery, with electrons leaving the anode and oxygen being absorbed at the cathode. Lithium has high specific capacity (3862 mAh/g) compared with other metal-air battery materials (820 mAh/g for Zinc, 2980 mAh/g for aluminum) making lithium an excellent choice for an anode material. At the cathode, reduction occurs by the recombination of lithium ions with oxygen. Currently, mesoporous carbon has been used as a cathode material with metal catalysts. Metal catalysts incorporated into the carbon electrode enhance the oxygen reduction kinetics and increase the specific capacity of the cathode. Manganese, cobalt, ruthenium, platinum, silver, or a mixture of cobalt and manganese are currently selected as metal elements of the catalysts, and their oxide, sulfide and cyclic compounds such as phthalocyanine are used in the cathode.
The Li-air cell performance is generally limited by the efficiency of reaction at the cathode because most of the cell voltage drop occurs at the cathode. Currently, multiple battery chemistry delineated by aprotic and aqueous electrolyte choice is employed in Li-air batteries, so the exact electrochemical reaction at the cathode varies between Li-air batteries. The aprotic design can include a lithium metal anode, a liquid organic electrolyte, and a porous carbon cathode, as a result, the main reaction chemistry is the deposition and decomposition of the insoluble lithium peroxide (Li2O2) or lithium oxide (Li2O). The aqueous Li-air battery can include a lithium metal anode, an aqueous electrolyte, and a porous carbon cathode. The aqueous electrolyte is simply a combination of lithium salts dissolved in water. This is a different reaction chemistry from the organic electrolyte system, that is the precipitation and decomposition through a form of soluble lithium hydroxide (LiOH).
While metal-air batteries, such as Li-air batteries are a promising post lithium ion battery technology, and Li—O2 versions of the battery are a promising candidate of high energy density type rechargeable batteries, the use of ambient air as a reactive gas instead of pure oxygen (O2) gas causes the battery to have poor recharging characteristics. This is because H2O and CO2 cause the inactivation of the reaction products such as Li2O2, Li2O and LiOH, that is the formation of Li2CO3, an inactive material for recharging. Ambient air including O2 gas is the most attractive active material, however ambient air impurities, H2O and CO2 degrade the huge advantage of Li—O2 batteries. An approach to overcome the impurities from ambient air is purifying H2O and CO2 from the ambient air with a form of air management to implement the gas purification. The complete gas management of impurities in ambient air is quite difficult even using state-of-the-art technology such as a gas separation membrane. Even though gas absorption technology using absorbents such as zeolite will eliminate most of the H2O and CO2 from ambient air, such a gas absorption system would have to be quite large to completely eliminate the impurities. Therefore, complete ambient air purification is often not realistic for most battery applications.
Albertus et al. in U.S. Patent Publication 2012/0094193 discloses a high specific-energy Li—O2/CO2 battery where ambient air including CO2 is introduced into Li-air batteries. In particular, a stoichiometric ratio of carbon dioxide (CO2) to oxygen of 2:1 is most favorable to achieve high energy density as a primary battery. However, in the current living environment, it is very difficult to concentrate CO2 gas up to the molar feed ratio of 2:1 relative to O2, because in ambient air the quantity of CO2 is about 0.03%, and a management system that maintains a constant CO2 concentration is difficult to implement since the CO2 concentration fluctuates in ambient air. Thus, for automobile use, the proposed battery is not realistic.
Thus, there exists a need for metal-air batteries that do not require complete purification of ambient air, and that are scalable for transportation and automotive applications.